1. Field of the Invention
The present invention relates to a device and a method for monitoring breathing, and more particularly, to a stress detecting device for a sensor utilizable in the monitoring of breathing.
The invention is applicable for monitoring patients in hospitals; for monitoring vital signs under field conditions; as an additional channel to be utilized with portable volume ventilators; for monitoring apnea, as well as to be used in conjunction with health-care devices dedicated to breathing and relaxation exercises and for educational purposes, including interactive computer games that involve respiration functions.
2. Discussion of the Prior Art
Various devices are known and used for monitoring respiration by means of rhythmic variations in the circumference of the chest or abdomen that accompany the breathing movements of a user. For motionless users such as anesthesized patients, most types of respiration sensors work satisfactorily. There is, however, an increasing need for low-cost respiration monitors for awake and even moving users, for example:
a) Monitors utilized in conjunction with portable volume ventilators, to be used at home by patients suffering from chronic lung diseases requiring, for safety purposes, an independent channel for monitoring respiration; PA1 b) Apnea monitors for home use; PA1 c) Other types of healthcare products that involve a respiration monitor; PA1 d) Computer-based educational products, which are based on multichannel monitoring of physiological variables, also including systems used for biofeedback processes, and PA1 e) Vital sign monitors to be used for mass casualties under field conditions, especially in case of, e.g., poisonous gases which were inhaled by patients that can cause severe breathing problems. This application requires the sensor used to minimize effects resulting from the movement of patients, which is unavoidable during transportation.
Most of the commercially available respiration sensors convert the rhythmic variations in the circumference of the chest or abdomen that accompany the breathing movements, into measureable electric signals. For example, known sensors measure variations of impedence between ECG electrodes attached to the chest, transient voltage or resistance changes generated, respectively, by piezoelectric or piezoresistive transducers, compressed or stretched by an elastic element, such as a belt or a sticky strip worn on the chest or abdomen, or by an elastic material on which the transducer is mounted.
The main problem with the known sensors is their great sensitivity to body movements not associated with respiration. This problem imposes serious limitations of the applications hereinbefore described. Hence, the problem of reducing the sensitivity of belt-type respiration sensors utilizing transducers to body movements of the measured signals requires the filtering out of undesired components, from the overall signals representing stresses applied by the belt to the transducer, in order to obtain a satisfactory sensor providing a reliable device for monitoring respiration.